I'm in the same situation, and it's rubbish!!
I have a client who's nails I have shellac'd twice previously and it has lasted beautifully for 16 days with no chips.
I did her nails on the 16th (Wed) of this month and they looked great.
Get a text from her on the following Monday saying she's lost one and can I fix it for her? As it was only 1 and the first time any of my clients have had a problem I agreed. She told me it had lifted on the Friday and she was just holding it down, but she went for a spray tan on the Friday and they put a barrier cream on her nails (quite rightly), so could it be that? I said possibly, if the barrier cream had got between the shellac and the nail plate then it could have helped with the lifting.
When I saw her on Tuesday the shellac had obviously been peeled off, which she admitted, but only because it was not really attached and was annoying her!
I fixed it and she went away happy.
I then get a text on Saturday morning saying she has "lost" another 2 nails, and she thinks they need to go - only appointment I have is today at 5pm which she says she'll take, so I booked her in.
I then get a text an hour later saying another 2 have gone, and she can't wait to be rid of them, which I didn't reply to as I was at work.
Then yesterday morning at 7.45am I get another text saying she doesn't need the appointment now as they have all fallen off!!
I cancelled the appointment for her and told her to make sure she uses her solar oil as there will be damage to her nail plate from peeling off the shellac, which she didn't deny, and that unless she has any other information for me about what she has been doing or if she has used any medication she hasn't told me about, then unfortunately I don't have an answer for her without seeing them.
She just said it's one of those things and she'll probably contact me next time she has a special occasion.
Ordinarily I would just let the situation slide, but she is one of a group of ladies who all know each other that I have built up a strong client base through, and i'm really worried she might bad mouth my work, and indirectly turn people away from me.
My business is finally starting to take off, and if I lose these clients now it will be a big hit to me.
I totally know how you feel O.P!!